On Friday, May 22, 2020 at 10:31:27 AM UTC-4, kinsell wrote:
On 5/18/20 5:27 PM, wrote:
On Monday, May 18, 2020 at 6:16:48 PM UTC-4, John Foster wrote:
I'm looking for a good charger for my PowerSonic AGM batteries. I have a car charger, but that seems to be malfunctioning, as it doesn't seem to want to charge car batteries or my glider batteries. Any recommendations on a good charger for these type of batteries?

There are so many charger models... I've found that some of them don't quite function as promised, or only work well with certain size batteries. So they should be monitored by a human. E.g., one small cheap charger that was supposed to be smart, when connected to a 12AH battery, never reached the point when it switches from "constant voltage" (about 14.5V) to "float" (about 13.5V), perhaps because the charge current at the high constant voltage never decreased enough in its "view". As a result, the battery got hot, meaning it was overcharged - which cuts short its lifetime.

Sounds like that battery had a shorted cell before the charging started.
Not common, but it happens. You can just put 14.4 volts on a good
battery, it will be fine, won't overcharge or get hot.




If you are not in a hurry, a charger that never gets to a voltage higher than 13.8 or so is safe, but leave the battery connected at least overnight to get more or less fully charged.

Don't use 13.8 to try to charge, use 14.4 and get a full charge. SLA's
aren't hard to charge.



Meanwhile, SLAs are rapidly becoming obsolete, as LiFePO4 battery prices are falling. Since the latter last about 3 times as many years, they are now cheaper per year, and they have many other advantages. How to charge them is a whole 'nuther topic. Which we may or may not want to drift into here in this thread?


SLA's last a long time, if you take care of them properly. LFP's don't
really save money, and if you burn up your glider, you might find
they're a bad deal.

The SLA in my story did NOT have a shorted cell. I know that from measurements and from charging it with other chargers. That specific charger just wasn't smart enough. The transition from high constant voltage to float happens when the charger sees the current accepted by the battery at the constant voltage (around 14.4V or so, some chargers go higher than that) reduces to some level. My guess is that in this case the current never reduced enough to satisfy this charger. I blame that on the battery being largish (12AH) and the charger being designed for somewhat smaller batteries. A constant overcharge all night caused the battery to heat up.

It the experience of most of us that SLAs in glider use only last between 2 and 5 years. At that point they may still "work" but the measured capacity is a fraction of the nameplate. LFPs have been shown to last much longer, at least 6 years, perhaps 10, and still have most of the nameplate capacity. Moreover the usable capacity of LFPs is the whole thing, while with SLAs you want to avoid discharging them much below halfway, or else their life gets shorter yet. Moreover, the output voltage of LFP stays near 13V for most of the discharge, so radios and such are happier.

BTW there is somebody on ebay right now selling PowerSync brand 12V 7.5H LFPs for about $35 shipped (in the USA), which is not much more than the price of a similar size SLA. I have no connection to the seller, but did buy 4 of them recently, and they tested good. Opened one up (was going to fit the innards into some other battery box, not in a glider) and found that it has a full BMS including temperature sensor and cell balancing. The only catch: these are "new" but were manufactured in the fall of 2017. Other sellers offer LFPs around $50.

I've stuck with SLAs up through the 2018 season, but their time has now passed. I love how my 12AH LFP seems like it has infinite capacity. In my glider, I don't need to worry about its charge lasting, not even if I forget to charge it and fly a second long flight on the same.

I have never heard of an LFP battery causing a glider fire? But I have heard several stories of fires caused by SLAs.